Tannemyer et al. in U.S. Pat. No. 6,081,383 teaches a multi-color, pattern-projecting gobo in which a multi-color pattern that is color-separated into single-color components that are disposed to parallel planes in the gobo and at least two of these planes are mutually separated by means of a transparent substrate. Such a gobo may include a plurality of mutually superimposed disc-shaped and transparent substrates each of which may include a dichroic surface coating so as to form a color filter. Thus combinations of the filters are able to reproduce the colors of the multi-color pattern and respective color-emitting surface coatings present a pattern that coincides with the pattern of corresponding color components in the multi-color pattern. The technical advance in the art contributed by this teaching, although not stated per se therein, allows the use of extremely thin substrates thereby vastly improving the focus of the entirety. In the prior art, in which the substrates are thicker, only one image-creating surface is in true focus.
Nevertheless, the gobo made according to Tannemyer et al. has certain deficiencies, which derive from the technique used in bonding the substrates together. The patent discloses a stepped profile assembly in which each successive layer of disc-shaped transparent pattern-bearing substrates is of smaller diameter than the preceding substrate. The patent teaches gluing the discs together by placing glue on the steps. In actual practice, as a person of skill in the art knows, the stepped profile is eliminated except after the initial substrate, the one carrying a blocking pattern. The color separation substrates are all of the same smaller diameter and the glue binding them together while applied around the circumference of the interface is applied in spaced dots of glue. Dots of the adhesive are placed around the edges of unbonded layers and then the next layer is aligned and placed on top to be adhered. Ordinarily the glue used is Dow Silicone # 732 or equivalent (available from Dow). This is a very viscous silicone product. The dotting of glue is important with these bonding techniques. This adhesive polymerizes under the action of the moisture contained in the ambient air. The reaction produces acetic acid, which must be removed by migration. The dots have a large surface area in relation to volume, which facilitates this process. In addition, the dots need to be close to the edge of the layers. The dots also present a minimized area of viscous adhesive, which permits the layers to be moved prior to polymerization to obtain perfect alignment. When a typical gobo is finished (such as those obtainable from Beacon AB of Sweden or their licensees) it contains four layers, adhered with three layers of edge dots of silicone.
There is, however, a negative aspect to this technique: The center of the gobo has air spaces and the layers can flex under load and cause breakage because of this weakness. Moreover, the structure is highly sensitive to impacts. Further, dust, dirt and other unwanted contaminants can work into these air spaces and render the gobo unusable or at least require that compressed air be blasted into the spaces to remove the contaminants. Sometimes even this type of cleaning does not solve the problem and the gobo is rendered useless. In the course of ordinary service, the life of a gobo so made is limited.
It is the object of the invention to improve the service life of gobos of the type taught by Tannemyer et al. by eliminating entrapment of air between facing substrates of the gobo and preventing the incursion of contaminants into the interfaces between layers.